Did you know that newborns sometimes vomit blood, even when perfectly healthy?

I sure didn’t, nor did my sister. So when this happened, she took her newborn daughter straightaway to the doctor. He explained that this was likely due to my niece having swallowed blood during the birthing process, and in fact nothing to be alarmed about. “How long does this last?” she asked anxiously. “Up to about seven days,” he noted.

I did some more investigation and learned that, indeed, the most likely cause of blood in a newborn’s vomit is “maternal blood”, either swallowed during delivery or from “cracked, raw nipples from breastfeeding”. (Ouch.) While the blood can come from the baby itself, this is actually much less common (although I didn’t find any stats on it); “The Newborn Child” by Johnston et al. agrees. Here’s an interesting case-study-esque version of how a doctor might diagnose such cases. It also describes the diagnostic test (“Apt test”) that is used to determine whether the blood is from the mother or the baby (the latter contains “fetal hemoglobin”). Rather than just citing the name of the test, the same source actually tells you how it works: mix the blood sample with sodium hydroxide, which breaks down adult hemoglobin (turning the sample dark brown) but will have less impact on fetal hemoglobin (which will stay pink). I really appreciate sources (particularly medical ones) that bother to explain the science behind the process, diagnosis, or treatment!